The process industry employs process variable transmitters to monitor process variables associated with substances such as solids, slurries, liquids, vapors, and gasses in chemical, pulp, petroleum, pharmaceutical, food and other processing plants. Process variables include pressure, temperature, flow, level, turbidity, density, concentration, chemical composition and other properties. A process fluid temperature transmitter provides an output related to a sensed process fluid temperature. The temperature transmitter output can be communicated over a process communication loop to a control room, or the output can be communicated to another process device such that the process can be monitored and controlled. In order to monitor a process fluid temperature, the transmitter includes a sensor, such as a resistance temperature device (RTD) or thermocouple.
One specific type of temperature transmitter is known as a head-mount temperature transmitter. Such a transmitter generally includes a connection head or junction box that is ruggedized for exposure to harsh environments. The connection head can be designed in accordance with the criteria of current DIN standard 43 729 Form B. Such design is relatively smaller than other process variable transmitter enclosures. The smaller design facilitates transmitter mounting in crowded installation environments. Further, the smaller design also provides a smaller mass coupled to the sensor probe. Such mass reduction reduces the possibility of vibration damage occurring in the transmitter.
The connection head, or junction box can be explosion-proof in conformance with NEC Sections 500-503, dated 1996. Typically, an electronics module is placed within the connection head and mounted with fasteners to provide a transmitter that is highly modular. Such modularity facilitates transmitter configuration changes as well as maintenance. An example of such a head-mount temperature transmitter is the Model 248 Temperature Transmitter available from Rosemount, Inc. of Eden Prairie, Minn.
This connection head size limitation puts severe constraints on the types of lead connections that are available within the transmitter. Traditionally, terminal blocks have been used for connecting sensor, communication, and/or power leads to the transmitter electronics itself. Additionally, some known compact temperature transmitters also provide external lead attachment clips to facilitate the attachment of external leads by a technician to the electronics module for maintenance and/or diagnostics. These known attachments have suffered from certain drawbacks.
Known external lead attachment clips have generally undesirably expanded the physical envelope of the electronics package. This is because such clips generally provided additional metallic loops which extend beyond the diameter of the electronics package. In industrial processing control environments employing compact transmitters such as those which comply with DIN standard 43 729 Form B, such expansion of the physical envelope is highly undesirable.
The provision of a compact process transmitter that is able to comply with the stringent space constraints of DIN standard 43 729 Form A or Form B while facilitating lead attachments and while providing external lead attachment clips that do not undesirably expand the physical envelope of the electronics module would be desirable to the art.